1. Field of the Invention
The present invention relates to circuits for fast turn-on/off in energy efficient Ethernet systems.
2. Description of the Related Art
Energy Efficient Ethernet (EEE) is a technique that causes transition of an Ethernet device between Active and Low Power Idle (LPI) states. The LPI state is a low power consumption state, and a device transitions to the LPI state based upon network demand. For EEE, the Ethernet network transmits data as fast as possible in the active state, then transitions to LPI to save energy. EEE is presently under study for standardization for Ethernet networks by the Institute of Electrical and Electronic Engineers (IEEE) committee 802.3az. The standardization process is specified for 100BASE-TX (Full Duplex), 1000BASE-T (Full Duplex), 10GBASE-T, 10GBASE-KR, 10GBASE-KX4, and 1000BASE-KX Ethernet networks, but the principles can be extended to all Ethernet networks.
During LPI, power consumption is reduced by turning off unused circuits. Consequently, transmit and receive data paths are turned off, parameters such as adaptive coefficients of filters and equalizers are stored, timing circuits are allowed to run free, and a refresh process is employed to periodically refresh timing and update parameters to ensure that that the circuitry might return to an active state with a relatively short initialization process. Using an OSI model, the MAC layer requests the PHY layer to enter or exit LPI. As proposed, the PHY sends Sleep Symbols for a fixed duration (“a sleep time”), upon which the PHY layer goes into a Quiet duration, which is a period of low power consumption. Periodically, the PHY layer temporarily “wakes-up” and enters Refresh duration, during which the PHY layer transmits Refresh Symbols for timing recovery and parameter synchronization. Upon request by the MAC layer, or if activated by received data, the PHY layer enters a Wake duration, during which time transmit and receive paths are activated, but no data is transmitted or received in order to give the system time to wake-up and transition fully to an active state.